Monitoring Methods and Designs for Evaluating Bioretention Performance

Roadside bioretention systems, also known as green streets are becoming increasingly popular, and have widespread potential to reduce pollutant loads coming from road runoff. However, the installation of these systems is outpacing the research regarding the comparative effectiveness of specific design features. Monitoring is a required component of many stormwater regulatory programs, and can provide vital feedback to designers and engineers, lower costs, and determine long-term effectiveness and maintenance requirements, yet very few bioretention systems are monitored. For professionals that are interested in performance assessment, there are very few descriptions of monitoring infrastructure for small drainage areas that are detailed enough to replicate during new bioretention construction projects. This research describes the innovative infrastructure used at the University of Vermont (UVM) Bioretention Laboratory to accurately measure pollutant mass load reduction by roadside bioretention systems. The inflow and outflow monitoring infrastructure designs are provided in enough detail to be adapted and/or replicated in other field settings. The steps taken to integrate the infrastructure into new construction are also provided. Ninety degree v-notch and compound weirs were installed at the inflow and outflow of eight bioretention systems, respectively. Differential pressure transducers related water height to flow rate. A time-based discrete sampling methodology was tested and found to adequately sample multiple points throughout the inflow and outflow hydrographs. This allowed for the comparison of pollutant mass removal among different bioretention designs on an equal volume basis.